In this article we formulate the moiré fringes that are formed by over laying two similar networks of points that the parameters of one of them suffers small collective defects. It is shown that the resulted moiré fringes can be described by quadratic functions. Therefore, any 2-D physical phenomenon that can be converted into the changes of the parameters of a network can be studied by the moiré technique. We have tested the approach by presenting some examples of superimposing defected networks on the similar networks free from defects.